A power transmission apparatus mounted on a hybrid vehicle is conventionally known.
For example, Japanese Patent Laying-Open No. 2002-274201 (Patent Document 1) discloses a power transmission apparatus including a power synthesizing mechanism connected to an electric motor and a generator to allow power transmission, and a transmission mechanism that changes the rotational speed of the electric motor for transmission to the power synthesizing mechanism. The ring gear in the power synthesizing mechanism and transmission mechanism is formed at the inner circumference of the same annular member.
Japanese Patent Laying-Open No. 2004-66898 (Patent Document 2) discloses a hybrid driving device including first and second electric motors and a planetary gear for power distribution. The planetary gear for power distribution includes a first rotary element to which the engine output is transmitted, a second rotary element that rotates in cooperation with the first electric motor, and a third rotary element that rotates in cooperation with the output unit. The transmission device is provided between the second electric motor and the output unit.
Japanese Patent Laying-Open No. 2004-340010 (Patent Document 3) discloses a power transmission apparatus of a hybrid vehicle including an engine, first and second motor generators, and a power split device. In this apparatus, the engine, the output gear wheel, and the two motor generators are arranged in this order.
Japanese Patent Laying-Open No. 2001-246953 (Patent Document 4) discloses a hybrid driving device including an engine, a generator, a planetary gear connecting the same, an electric motor, and a differential mechanism. In this hybrid driving device, the output unit of the planetary gear is separated from the output unit of the electric motor.
Japanese Patent Laying-Open No. 8-318746 (Patent Document 5) discloses a hybrid unit mounted on a hybrid vehicle. In this hybrid unit, the bearing that supports the rotor is provided at the outer circumference of the shaft that is arranged concentric with the rotor.
The power transmission apparatus disclosed in Patent Document 1 has the power synthesizing mechanism and transmission mechanism formed integrally. Motive power is output towards the output shaft from the annular member (ring gear) constituting the power synthesizing mechanism and transmission mechanism. Since the annular member is provided between the electric motor and the generator, it is difficult to form the housing of the electric motor and the housing of the generator integrally. Further, a bearing of a relatively large diameter must be provided in order to support the annular member. Accordingly, eccentricity and unbalance will readily occur at the annular member that is an internal component. This causes increased noise to induce the possibility of variation in intensity. Critical techniques in the production stage are required to suppress such problems, which will degrade the productivity of power transmission apparatuses. It can be said that the configuration of solving such problems is not sufficiently disclosed in Patent Documents 2-5.
There is also a problem that down-sizing of the drive unit is inhibited for the power train in the case where a plurality of rotating electric machines are provided and the bearing to support the rotors thereof is attached to a fixture support in the housing. This is because the space to dispose the fixture support and the bearing at both sides of each rotating electric machine is required. In the case where the aforementioned support is provided so as to protrude inwards of the rotor core from the standpoint of reducing the entire length of the drive unit, the support must be formed in a complicated configuration, resulting in degradation of the productivity of the drive unit. It can be said that a configuration of solving this problem is not sufficiently disclosed in Patent Documents 1-5. For example, the unit disclosed in Patent Document 5 has the bearing that supports the rotor of the rotating electric machine attached to the support member affixed to the housing.